1. Field
The present invention relates generally to data communication, and more specifically to techniques for acquiring the frequency of a pilot in a wireless (e.g., CDMA) communication system based on a window of data samples.
2. Background
Wireless communication systems are widely deployed to provide various types of services such as voice, data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or some other multiple access techniques. CDMA systems may provide certain advantages over other types of system such as increased system capacity. A CDMA system is typically designed to conform to one or more standards, such as IS-95, IS-2000, IS-856, W-CDMA, and TS-CDMA standards, all of which are known in the art and incorporated herein by reference.
A terminal in a CDMA system needs to acquire signals transmitted from one or more base stations in order to receive or exchange data. In many CDMA systems, a pilot is transmitted from each base station to assist the terminals perform a number of functions. The pilot is typically generated based on a known data pattern (e.g., a sequence of all zeros) and using a known signal processing scheme. The pilots from the base stations may be used at the terminals for acquisition, frequency and timing synchronization, channel estimation, coherent data demodulation, and so on.
The acquisition of a pilot is made challenging due to various phenomena. First, the pilot is distorted by noise and interference in the communication link, which can make detection of the pilot difficult at a terminal. Second, the received signal at the terminal typically includes multiple pilot instances at various amplitudes, phases, and delays due to a multipath environment. Third, since the terminal may not be certain of its frequency relative to that of the system, the received signal may be downconverted with a frequency error that needs to be determined and corrected before demodulation and other processing may be performed. Fourth, for certain situations such as when processing a quick paging channel (QPCH), the data of interest may reside in short bursts, and only a window of data samples covering a short time period may be available for pilot acquisition.
There is therefore a need in the art for techniques to acquire a pilot in a wireless (e.g., CDMA) communication system based on a window of data samples.